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Wednesday, January 26, 2011

Two recently released studies in weather patterns concern Western mountainous regions of the U.S. and a third report relates to Iowa weather. Both the California and Iowa reports indicate wetter trends.

A study in the journal Science challenges assumptions that climate change and rising temperatures would send vegetation to higher elevations. ....But comparing data from the early and late 20th century, authors of the Science paper found that despite warming, many plant species in California mountain ranges are growing at lower elevations than they did 80 years ago. The scientists attributed the shift to a wetter climate in Central and Northern California, which offset the effect of higher temperatures. The lesson, said coauthor John Abatzoglou, a University of Idaho assistant geography professor, is that "we'd be remiss if we just focus on temperature," in forecasting the influence of climate change on plant life. "This might mean species extinction rates may not be as dire as predicted."

...For whatever reason, Abatzoglou said the Sierra was 5% to 10% wetter in the final half of the 1900s than in the first half, allowing tree and shrub species to take hold at lower elevations. Comparing historic vegetation data from 1905 to 1935 to information gathered from 1975 to 2005 by researchers and federal agencies, the study found that about five dozen species had on the whole migrated downhill an average of about 264 feet.

More than 50 years of records in the western mountains of the United States show that while it is now significantly warmer, total annual precipitation has not changed. But a system that was once dominated by winter snowfall now experiences a mix of rain and snow, with more streamflow in winter and less in spring. As a result, there is less water for ecosystems and agriculture during the spring and summer growing season. These changes make forecasting and managing western water resources more difficult and present a serious challenge to agriculture in the region.

...not only is streamflow occurring earlier, but more of the annual flow is concentrated in the March–June period, leaving even less for the dry summer growing season,” Marks says. “In the mountains of the West,” Marks says, “the seasonal snow cover is Nature’s reservoir, storing water from winter snowstorms for release to the soil and streams during spring and early summer. Water resource management in the West is based on a reliable spring rise in streams from snowmelt. If, as we have observed in the Reynolds Creek Experimental Watershed, this system is changing, then our ability to effectively forecast water supply for the region is uncertain.

He said Iowa will sit astride a wet/dry dividing line that will make the southern half of the United States drier than usual but leave Iowa north of U.S. Highway 20 with adequate or greater-than-usual moisture. "We won't have a drought," Anderson said. Unusual weather conditions have beset Iowa in recent years, including extra-wet springs for three years beginning in 2007, followed by last year's dry spring; a record wet October in 2009 that delayed harvests until Thanksgiving or later; and then an unusually wet July last year that is credited with cutting Iowa's corn yield for 2010 by 9 percent from the previous year. Anderson said records show larger and more intense rains in Iowa since 1960. "We know that we are getting more moisture than in the first half of the 20th century," he said.